The flow-rate sensor outputs the electrical signal depending on the flow-rate of the air and the electrical signal is converted into the flow-rate by the converting characteristic for the output-and-flow-rate (hereinafter referred to as a converting map).
The converting map is memorized in a memory device of an electronic control unit (ECU), which is communicated with the flow-rate sensor. The electrical signal from the flow-rate sensor is converted into the flow-rate by the ECU based on the converting map.
The flow-rate measuring apparatus is applied to, for example, an engine control system for a vehicle, in particular, to an intake air amount measuring apparatus for the engine. The flow-rate measuring apparatus measures a flow-rate of the intake air, which flows in an intake air passage from an upstream side toward a downstream side thereof. The flow of intake air from the upstream to the downstream side is referred to as a forward air-flow, while the flow of the intake air from the downstream to the upstream side is referred to as a backward air-flow. In the flow-rate measuring apparatus, which is capable of measuring the flow-rate of not only the forward air-flow but also the backward air-flow, the converting map is divided into a part for the forward air-flow and a part for the backward air-flow.
A flow-rate measuring apparatus of a prior art, for example, as disclosed in Japanese Patent Publication No. H09-15013(A), has a converting map (for the forward air-flow and backward air-flow), as shown in FIG. 9, which is prepared based on a relationship between an electrical output of a sensor and a flow-rate, wherein the electrical output is obtained in a static property when the sensor is placed in a static air-flow condition.
However, in an actual measuring situation, the backward air-flow actually generated in a bypass air passage is an instantaneous variation of the air-flow. Accordingly, when the converting map of FIG. 9 (which is prepared on the premise of the static property) is used, a measurement error may occur in an area of the backward air-flow.
According to the flow-rate measuring apparatus of the above prior art, the converting map is corrected when it is used. However, such a process for correcting the converting map is complicated. Therefore, it is desirable to reduce the measurement errors in the area of the backward air-flow without correcting the converting map.